Phage Susceptibility and Enterotoxin Production by Staphylococcus aureus Strains Isolated from Nigerian Foods

The sensitivity of Staphylococcus aureus strains isolated from Nigerian foods to phages in the international phage sets for typing human and bovine strains of staphylococci was determined. The enterotoxigenicity of the strains was also determined using the avidin-biotin enzyme-linked immunosorbent assay and the reversed passive latex agglutination test (for staphylococcal enterotoxin D only). One hundred and five (67.7%) of 155 strains tested were susceptible to phages in both typing sets. Phages for staphylococci of human origin lysed all 105 typeable strains while those for staphylococci of bovine origin were responsible for the lysis of 92 strains. Phages in the different phage groups (mixed) were most frequently responsible for lysis, 29 (27.6%), followed by group III phages with 26 (24.8%) strains susceptible. Of the 155 strains tested, 122 (78.7%) were enterotoxigenic producing staphylococcal enterotoxins A, B, C, D, or a combination. Dried beef isolates were most enterotoxigenic (100.0%) and those from fermented milk least (68.8%). Staphylococcal enterotoxins C, B, and A were elaborated either singly or in combination by 71 (58.2%), 69 (56.6%), and 62 (50.8%) strains, respectively. It was concluded that a majority of staphylococcal strains isolated from Nigerian foods originated from humans and their high enterotoxigenicity could be a health risk to consumers.